1. Field of the Invention
The present invention relates to an EL (electro luminescent) element drive circuit and a propriety test method for drive currents of the same organic EL element drive circuit and, in particular, the present invention relates to an organic EL display element drive circuit (driver IC), which generates drive currents to be supplied to terminal pins of an organic EL display panel by converting digital values into analog drive currents by D/A converter circuits and is capable of effectively testing the analog drive currents to be outputted from output pins of the driver IC to the analog respective terminal pins for the propriety thereof.
2. Description of the Prior Art
An organic EL display panel of an organic EL display device, which is mounted on a portable telephone set, a PHS, a DVD player or a PDA (personal digital assistance) and includes 396 (132×3) terminal pins for column lines and 162 terminal pins for row lines, has been proposed and the number of column lines and the number of row lines of such organic EL display panel tend to be further increased.
An output stage of a current drive circuit of such organic EL display panel includes output circuits of, for example, a current-mirror circuit, which are provided correspondingly to respective terminal pins of the organic EL display panel, regardless of the type of drive current, the passive matrix type or the active matrix type.
For example, JP2003-308043A and JP2003-308044A disclose organic EL element drive circuits in each of which D/A converter circuits are provided in an upstream side of respective current mirror output circuits and drive currents to be supplied to respective terminal pins of an organic EL display panel are generated by converting digital display data for terminal pins of the column side into analog drive currents by means of the D/A converter circuits.
Further, JPH9-232074A discloses an organic EL element drive circuit in which organic EL elements arranged in a matrix are current driven and are reset by grounding anodes and cathodes of the organic EL elements. Further, JP2001-143867A discloses a technique with which organic EL elements are current-driven with low power consumption by using DC/DC converters.
The increase in number of terminal pins of the organic EL display panel results in an increase of time required to test a column driver IC for the propriety of the drive currents to be supplied to the respective terminal pins, that is, for whether or not the drive currents supplied to the respective terminal pins are appropriate. Further, due to the increase in the terminal pins, a plurality of column driver ICs are necessary on the side of the column line. In an organic EL element drive circuit of QVGA full color system, for example, 120 terminal pins are necessary for each of R, G and B display colors, so that a total of 360 terminal pins and hence 3 column drivers are necessary nowadays. Therefore, the number of the column driver ICs to be tested tends to be increased.
Further, the column driver IC, which generates drive currents by converting digital display data into analog values by means of D/A converter circuits, has to be tested for whether or not it can normally generate drive currents correspondingly to the display data from the minimum value (all bits are “0”) to the maximum value (all bits are “1”). Therefore, the test time required in the test step of the column driver ICs is increased, resulting in degradation of throughput of fabrication of the column driver ICs.